1. Field of Invention
The present invention relates to a kind of anode material of a lithium ion battery, its preparation method thereof and a lithium ion battery which utilize the anode material, and more particularly to a cobalt-nickel-manganese ternary material and its preparation method, and a lithium ion secondary battery which make use of the cobalt-nickel-manganese ternary material.
2. Description of Related Arts
Since Lithium-ion battery has been commercialized in 1991, its application requirements are increased continuously, and its energy density requirement has also increased with the market development. Specifically, the energy density of lithium-ion battery can be divided into mass density and bulk density, and the market requires the increase of both of the density by mass and the density by volume of the battery. Under the condition of providing a unit capacity, increasing the energy density of the battery means increasing the filling capacity of unit volume of the active substance of the battery. At present, the most widely used material is still lithium cobalt oxide. Lithium cobalt oxide is the earliest commercialized material, its application development is already mature and is widely used in many small scale low voltage portable electronic products such as mobile phone, laptop and digital electronic devices. However, since there is limited resources and higher safety requirement, a new research direction which focuses on providing a low cost, high energy density and high safety level battery without or with low content of cobalt for anode material of lithium battery has been developed. The continuous development has resulted in a cobalt-nickel-manganese ternary material and a manganese series material which has a capacity exceeding the lithium cobalt oxide and a safety level which is higher than the lithium cobalt oxide while the cost is lowered. However, certain discoveries are found during analysis of the ternary material: the discharging voltage of the ternary material is low, the compaction density of the electrode plate is low, which is lower than the compaction density of the lithium cobalt oxide, and therefore the single cobalt-nickel-manganese ternary material and the manganese series material cannot fulfill the market demand which requires high performance anode materials. The cobalt-nickel-manganese ternary material and the manganese series material cannot replace the conventional lithium cobalt oxide to use in the high end lithium-ion secondary battery. The conventional preparation method generally includes a machine for mixing two materials so that the cost is lowered and the safety is increased through providing the material mixture. For example, LiCoO2 and LiMn2O4 are the two mixing materials which are employed by SONY to solve the overcharge problem and improve the thermal stability. However, this simple act of physical mixing will affect the performance of the materials, for example, the compaction density is decreased accordingly and the volumetric capacity is only a direct average value of the two mixing materials.